The present invention relates to a display device, which utilizes an emission of electrons into a space which is in a vacuum state; and a method of fabrication thereof; and, more particularly, the invention relates to a display device having a high performance and a high reliability, in which the position and the size of electron sources can be established with precision, and, at the same time, deterioration of the characteristics of the electron sources can be prevented.
As a display device which exhibits high brightness and the high definition, color cathode ray tubes have been widely used conventionally. However, along with the recent desire for information processing equipment or television broadcasting that is capable of providing images of higher quality, the demand for planar displays (panel displays) which are light in weight and require a small space, while also exhibiting a high brightness and a high definition, has been increasing. As typical examples of such panel display devices, liquid crystal display devices, plasma display devices and the like have been developed. More particularly, as display devices which provide a higher brightness, it is expected that various other kinds of panel-type display devices, including a display device which utilizes an emission of electrons from electron sources into a vacuum (hereinafter referred to as “an electron emission type display device” or “a field emission type display device”) and an organic EL display device, which is characterized by low power consumption, will be put into practice.
Among panel type display devices, such as the above-mentioned field emission type display device, a display device having an electron emission structure which was developed by C. A. Spindt et al (for example, see U.S. Pat. No. 3,453,478), a display device having an electron emission structure of a metal-insulator-metal (MIM) type, a display device having an electron emission structure which utilizes an electron emission phenomenon based on a quantum theory tunneling effect (also referred to as a “surface conduction type electron source”, see Japanese Unexamined Patent Publication 2000-21305, for example), and a display device which utilizes an electron emission phenomenon having a diamond film, a graphite film and carbon nanotubes and the like have been known.
FIG. 11 is a cross-sectional view showing one example of a known field emission type display device. FIG. 12(a) and FIG. 12(b) are diagrams showing an example of an electron source of one pixel and a control electrode which controls the electron emission quantity of the electron source in the field emission type display device shown in FIG. 11. The field emission type display device is constituted such that, between inner peripheries of both of a back panel 100, having field emission type electron sources and control electrodes formed on an inner surface thereof, and a face panel 200, having anodes and fluorescent material layers formed on an inner surface thereof which faces the back panel 100 in an opposed manner, a sealing frame 300 is inserted and sealed so as to create an inner space which is defined by the back panel 100, the face panel 200 and the sealing frame 300. The pressure of this inner space is set to a value lower than the external pressure, or a vacuum is created in the inner space (with conditions hereinafter will be referred to simply as a “vacuum” state).
The back panel 100 includes a plurality of cathode lines 2, having electron sources disposed thereon, and control electrodes 4, which are configured to cross the cathode lines 2 and to be separated therefrom by way of insulating layers 3; and, these elements are supported on one surface of a back substrate 1, which is preferably made of glass or ceramics. In response to a potential difference applied between the cathode line 2 and the control electrode 4, the emission quantity (including turning on and off of emission) of electrons that are emitted from the electron source is controlled. Further, the face panel 200 includes anodes 7 and fluorescent materials 6 supported on one surface of a face substrate 5 that is made of a light transmissive material, such as glass. The sealing frame 300 is fixed to the inner peripheries of the back panel 100 and the face panel 200 using an adhesive material, such as frit glass. The inside space that is formed by the back panel 100, the face panel 200 and the sealing frame 300 is evacuated at a degree of vacuum of 10−5 to 10−7 Torr, for example. The gap between the back panel 100 and the face panel 200 is held by gap holding members 9.
The insulating layers 3 are interposed between the cathode lines 2, which are formed on the back substrate 1 of the back panel 100, and the control electrodes 4, which cross the cathode lines 2 and apertures (grid holes) 4a, are formed in respective crossing portions or regions of the control electrodes 4. On the other hand, the electron sources 2a are formed on the above-mentioned crossing portions in corresponding regions of the cathode lines 2, while the insulating layer 3 is removed at portions of the cathode lines 2 which correspond to the apertures 4a formed in the control electrodes 4. The apertures 4a allow the electrons emitted from the electron sources 2a to pass therethrough to the anode side.
The above-mentioned electron sources are constituted, for example, of carbon nanotubes (CNT), diamond-like carbons (DLC) or other field emission cathodes. Here, as the electron sources, sources which use carbon nanotubes (hereinafter referred to as a “CNT”) are employed. As shown in FIG. 12(a) and FIG. 12(b), the electron source 2a is arranged right below the aperture 4a of the control electrode 4. Although one electron source 2a is allocated to each one pixel in FIG. 12(a) and FIG. 12(b), it is also possible to allocate a plurality of electron sources 2a to one pixel.
FIG. 13(a) and FIG. 13(b) are diagrammatic views of a display device in which a plurality of electron sources are formed per one pixel. That is, FIG. 13(a) and FIG. 13(b) show an arrangement in which a plurality of small electron sources and small apertures are formed per one pixel. Here, a plurality of small apertures 4a1 to 4aN are formed in the control electrode 4 and a plurality of small electron sources 2a1 to 2aN are formed on the cathode line 2 at positions corresponding to the respective small apertures. The electrons irradiated from the back panel 100 impinge on the fluorescent material 6 that is formed on the face panel 200, which faces the back panel 100 in an opposed manner. Then, light which responds to the light emitting property of the fluorescent material 6 is irradiated to the outside of the face panel 200 so that the structure functions as a display device.
FIG. 14 is a diagrammatic cross-sectional view showing another example of a known field emission type display device which includes one electron source and one aperture per one pixel. Further, FIG. 15 is an enlarged cross-sectional view of the portion indicated by A in FIG. 14. In FIG. 14 and FIG. 15, reference symbol 100 indicates a back panel, reference symbol 200 indicates a face panel and reference symbol 300 indicates a sealing frame. The back panel 100 includes cathode lines 2, which have electron sources 2a disposed thereon, and control electrodes 4, which are provided in an insulated manner from the cathode lines 2 or an inner surface of the back substrate 1. In this example, the control electrodes 4 are held in such a way that the above-mentioned insulating layer 3 is not interposed therebetween. Further, on an inner surface of the face substrate 5, which constitutes the face panel 200, fluorescent materials 6 and anodes 7 are formed in the same manner as provided in the previously-mentioned display devices.
The control electrode 4 has the function of controlling the emission of electrons (pulling out of electrons) from the electron source 2a, which is arranged on the cathode line 2. Further, in place of the control electrode 4, or in addition to the control electrode 4, it may be possible to adopt a constitution in which another electrode is provided for applying a potential which converges electrons to the fluorescent material 6. Although the fluorescent material 6 is formed on the anodes 7 in FIG. 14, it is also possible to arrange the anode 7 so that it covers the fluorescent material 6. Further, it is also possible to provide a light shielding layer (black matrix) between the neighboring fluorescent materials 6. The back panel 100 and the face panel 200 are laminated to each other by a sealing frame 300 and the space defined between them is sealed in a vacuum.
As shown in FIG. 15, electron sources 2a are formed on the cathode lines 2 that are provided on the back panel 100. The electron source 2a is formed of an electron emitting material which efficiently generates electrons in response to an electric field applied between the cathode line 2 and the control electrode 4. With respect to a conductive material, in general, the sharper the shape of outside edges thereof which are exposed to the electric field, the higher will be the electron emitting performance exhibited by the conductive material. Accordingly, by adopting a fiber-like (rod-like) conductive material, it is possible to realize a highly efficient electron emission. As one example of such electron emitting materials, the above-mentioned CNT exists.
When a fiber-like conductive material is used as the material of the electron sources 2a, it is necessary to fix the conductive fibers on the cathode lines 2. Here, an explanation of how this is done will be made with respect to a case in which a CNT is used as the fiber-like conductive material. A CNT is an extremely fine needle-like carbon compound. In a strict sense, it is a hollow substance in which a planar structure called graphene, which is formed of carbon atoms arranged in a hexagonal shape, is arranged in a cylindrical shape and is closed and has a diameter on a nanometer scale. By arranging a CNT on the cathode line so as to use the CNT as an electron source, it is possible to obtain an efficient electron emission. In arranging the CNT on the cathode line, there is a known a method in which an electrode paste, which is formed by mixing the CNT together with a conductive filler, such as silver or nickel, is applied to the cathode line to form an electron source layer, and, thereafter, the electron source layer is baked so as to be fixed to the cathode line. Here, the following publications represent example which disclose the related art on this type of display device: Japanese Unexamined Patent Publication 11-144652, and Japanese Unexamined Patent Publication 2000-323078.